This study is aimed at increasing our understanding of the structure and mechanism of action of monoamine oxidase (MAO) in the CNS and in other animal tissues and of the mechanism of inhibition of the enzyme by substances of pharmacological interest. Efforts will be made to standardize procedures for the reproducible isolation of MAO from various tissues, including brain, and for determining the structural and functional differences between the A and B types in which the enzyme occurs. Additional studies will examine the functional role of the iron center, the mechanism of the irreversible inhibition of MAO by t-phenylcyclopropylamine, phenylhydrazine, and allenes, and the chemical reasons for the extreme lability of the cysteinyl riboflavin, the form of flavin at the active center of MAO, and the means by which the flavin is stabilized in peptide and in the native enzyme. Other studies will be aimed at defining the chemistry of the interaction between monoamines and the covalently bound flavin on the enzyme.